It is true that any shortcoming of God’s law offends against his perfect holiness and makes us liable to judgment, since God cannot look with favour on any sin (Habakkuk 1:13; James 2:10–11).
But what brought a person to ruin in the Old Testament (and it is the same for us today) was not the failure to have the righteousness of sinless perfection. What brought them to ruin was the failure to trust in the merciful promises of God, especially the hope that he would one day provide a redeemer who would be a perfect righteousness for his people (“the Lord is our righteousness,” Jeremiah 23:6; 33:16). The saints knew that this is how they were saved, and that this faith was the key to obedience, and that obedience was the evidence of this faith.
It is terribly confusing when people say that the only righteousness that has any value is the imputed righteousness of Christ. Clearly, justification is not grounded on any of our righteousness, but only on the righteousness of Christ imputed to us. But sometimes people are careless and speak disparagingly of all human righteousness, as if there were no such thing that pleased God.
They often cite Isaiah 64:6, which says our righteousness is as filthy rags, or “a polluted garment.” “We have all become like one who is unclean, and all our righteous deeds are like a polluted garment.”
But in the context, Isaiah 64:6 does not mean that all righteousness performed by God’s people is unacceptable to God. Isaiah is referring to people whose righteousness is in fact hypocritical. It is no longer righteousness. But in the verse just before this, Isaiah says that God approvingly meets “him who joyfully works righteousness” (verse 5).
It’s true — gloriously true — that none of God’s people, before or after the cross, would be accepted by an immaculately holy God if the perfect righteousness of Christ were not imputed to us (Romans 5:19; 1 Corinthians 1:30; 2 Corinthians 5:21). But that does not mean God does not produce in those “justified” people an experiential righteousness that is not a “polluted garment.”
In fact, he does, and this righteousness is precious to God and is, in fact, required — not as the ground of our justification (which is the righteousness of Christ only), but as an evidence of our being truly justified children of God.